Chemistry Reference
In-Depth Information
5.2 Microscopy Techniques
Microscopy techniques permit one to acquire important qualitative information
about the average length, morphology, thickness, and purity of CNTs. These
techniques are extensively used because of the large amount of data simultaneously
obtainable from a single image.
5.2.1 Atomic Force Microscopy
The major advantage of this technique is to provide accurate three-dimensional
topographic information.
AFM is suitable for the analysis of CNTs when they are homogeneously
dispersed and spin-coated in a convenient solvent at very low concentrations
(1
g/mL) in order to allow proper individualization and reliable measurement of
the size distribution (diameter and length).
AFM studies have allowed differentiation between SWCNTs and DWCNTs by
measuring the compressed height and the mechanical forces of the tubes squeezed
between an AFM tip and a silicon surface [
146
]. Moreover, several species attached
to CNTs, covalently or not, have been successfully identified using AFM: gold
colloids and silver clusters, magnetic nanoparticles encapsulated in carbon
nanotubes, biomolecules such as enzymes, BSA, DNA, etc. [
60
,
62
,
147
-
149
].
Among the many applications of this technique, one particularly interesting
relates to the use of CNTs as longlasting and mechanically non-invasive AFM
tips, opening the door to non-conventional microfabrication rules for better lateral
resolution [
150
].
μ
5.2.2 Transmission Electron Microscopy
When employed for the characterization of nanotubes, transmission electron
microscopy (TEM) reveals important details about dispersibility, purity grade,
size dimension, and a crude assessment of the functionalization in some cases
[
60
]. With the development of high-resolution TEM (HRTEM) techniques,
progress has been achieved towards the accurate assignment of chiral indices of
SWCNTs (Fig.
36
), which can be analyzed on the basis of the intensity distribution
on the main layer lines [
151
].
Impressive images provided by HRTEM allowed the identification of
one-dimensional arrays of C
60
inside SWCNTs, the so-called peapod structures,
and more recently, conformational changes of small hydrocarbon molecules con-
fined in carbon nanotubes were observed [
152
,
153
].
